Stability of Newton black films of highly fluorinated non-ionic surfactants

The aim of the present study is to present the new self-organization of various highly fluorinated non-ionic surfactants into freestanding Newton black films (NBF). The NBF are made of two surfactant walls with the polar heads turned toward the central core. We determine their molecular arrangement by means of X-ray reflectivity at grazing angles. This technique provides a determination of the electronic density profile perpendicular to the film and thus its structure. From a detailed analysis of this profile, we obtain the density, the thickness of the zone occupied by either the highly fluorinated chains or the hydrophilic groups and the quantity of water in the central core of the film. The great majority of our fluorinated surfactants were able to form black films. However, the introduction of a short hydrocarbon terminus on the hydrophobic tail destabilizes this structure and seems to inhibit the formation of the black film. The thickness of the aqueous phase mainly depends on the nature of the hydrophilic heads carried by the surfactants. (C) 2000 Elsevier Science S.A. All rights reserved.